Quaternary Science Reviews

Published by Elsevier
Print ISSN: 0277-3791
The climatic signal of Marine Isotope Stage (MIS) 11 is well-documented in marine and ice-sheet isotopic records and is known to comprise at least two major warm episodes with an intervening cool phase. Terrestrial records of MIS 11, though of high resolution, are often fragmentary and their chronology is poorly constrained. However, some notable exceptions include sequences from the maar lakes in France and Tenaghi Philippon in Greece. In the UK, the Hoxnian Interglacial has been considered to correlate with MIS 11. New investigations at Hoxne (Suffolk) provide an opportunity to re-evaluate the terrestrial record of MIS 11. At Hoxne, the type Hoxnian Interglacial sediments are overlain by a post-Hoxnian cold-temperate sequence. The interglacial sediments and the later temperate phase are separated by the so-called 'Arctic Bed' from which cold-climate macroscopic plant and beetle remains have been recovered. The later temperate phase was deposited during an episode of boreal woodland and is associated with the artefacts, a diverse vertebrate fauna and molluscs. New amino acid geochronological data and biostratigraphical considerations suggest that the post-Hoxnian sequence correlates with late substages of MIS 11. The paper further investigates the correlation of the sequence at Hoxne with the palynological sequences found elsewhere in Europe and adjacent offshore areas.
Multidisciplinary investigations of the vegetational, faunal and sea-level history inferred from the infills of buried channels on the coast of eastern Essex have a direct bearing on the differentiation of MIS 11 and MIS 9 in continental records. New data are presented from Cudmore Grove, an important site on Mersea Island that can be linked to the terrace sequence of the River Thames. The vegetational history has been reconstructed from a pollen sequence covering much of the interglacial represented. The temperate nature of the climate is apparent from a range of fossil groups, including plant remains, vertebrates (especially the rich herpetofauna), molluscs and beetles, which all have strong thermophilous components. The beetle data have been used to derive a Mutual Climatic Range reconstruction, suggesting that mean July temperatures were about 2 degrees C warmer than modern values for southeast England, whereas mean January temperatures may have been slightly colder. The sea-level history has been reconstructed from the molluscs, ostracods and especially the diatoms, which indicate that the marine transgression occurred considerably earlier in the interglacial cycle than at the neighbouring Hoxnian site at Clacton. There are a number of palynological similarities between the sequence at Cudmore Grove and Clacton, especially the presence of Abies and the occurrence of Azolla filiculoides megaspores. Moreover, both sites have yielded Palaeolithic archaeology, indeed the latter is the type site of the Clactonian (flake-and-core) industry. However, the sites can be differentiated on the basis of mammalian biostratigraphy, new aminostratigraphic data, as well as the differences in the sea-level history. The combined evidence suggests that the infill of the channel at Cudmore Grove accumulated during MIS 9, whereas the deposits at Clacton formed during MIS 11. The infill of a much later channel, yielding non-marine molluscs and vertebrates including Hippopotamus, appears to have formed during the Ipswichian (MIS 5e). This evidence is compared with other important sites of late Middle Pleistocene age in Britain and elsewhere on the continent and the importance of a multidisciplinary approach is stressed.
Quaternary climatic fluctuations have had profound effects on the phylogeographic structure of many species. Classically, species were thought to have become isolated in peninsular refugia, but there is limited evidence that large, non-polar species survived outside traditional refugial areas. We examined the phylogeographic structure of the red fox (Vulpes vulpes), a species that shows high ecological adaptability in the western Palaearctic region. We compared mitochondrial DNA sequences (cytochrome b and control region) from 399 modern and 31 ancient individuals from across Europe. Our objective was to test whether red foxes colonised the British Isles from mainland Europe in the late Pleistocene, or whether there is evidence that they persisted in the region through the Last Glacial Maximum. We found red foxes to show a high degree of phylogeographic structuring across Europe and, consistent with palaeontological and ancient DNA evidence, confirmed via phylogenetic indicators that red foxes were persistent in areas outside peninsular refugia during the last ice age. Bayesian analyses and tests of neutrality indicated population expansion. We conclude that there is evidence that red foxes from the British Isles derived from central European populations that became isolated after the closure of the landbridge with Europe.
Drill cores from the inner-alpine valley terrace of Unterangerberg, located in the Eastern Alps of Austria, offer first insights into a Pleistocene sedimentary record that was not accessible so far. The succession comprises diamict, gravel, sand, lignite and thick, fine grained sediments. Additionally, cataclastic deposits originating from two paleo-landslide events are present. Multi-proxy analyses including sedimentological and palynological investigations as well as radiocarbon and luminescence data record the onset of the last glacial period (Würmian) at Unterangerberg at ∼120-110 ka. This first time period, correlated to the MIS 5d, was characterised by strong fluvial aggradation under cold climatic conditions, with only sparse vegetation cover. Furthermore, two large and quasi-synchronous landslide events occurred during this time interval. No record of the first Early Würmian interstadial (MIS 5c) is preserved. During the second Early Würmian interstadial (MIS 5a), the local vegetation was characterised by a boreal forest dominated by Picea, with few thermophilous elements. The subsequent collapse of the vegetation is recorded by sediments dated to ∼70-60 ka (i.e. MIS 4), with very low pollen concentrations and the potential presence of permafrost. Climatic conditions improved again between ∼55 and 45 ka (MIS 3) and cold-adapted trees re-appeared during interstadials, forming an open forest vegetation. MIS 3 stadials were shorter and less severe than the MIS 4 at Unterangerberg, and vegetation during these cold phases was mainly composed of shrubs, herbs and grasses, similar to what is known from today's alpine timberline. The Unterangerberg record ended at ∼45 ka and/or was truncated by ice during the Last Glacial Maximum.
Few well-dated, quantitative Holocene temperature reconstructions exist from high-altitude sites in the Central Eastern Alps. Here, we present a chironomid-based quantitative reconstruction of mean July air temperatures (T(July)) throughout the Holocene for a remote high-mountain lake, Schwarzsee ob Sölden, situated above the treeline at 2796 m a.s.l. in the Austrian Alps. Applying a chironomid-temperature inference model developed from lakes of the Alpine region to a high-resolution chironomid record from the lake provides evidence for early Holocene (ca 10000-8600 cal yr BP) T(July) of up to 8.5 °C, i.e. >4 °C above the modern (1977-2006) mean July temperature. The reconstruction reveals the so-called '8.2-ka cold event' centered at ca 8250-8000 cal yr BP with temperatures ca 3 °C below the early-Holocene thermal maximum. Rather warm (ca 6 °C) and productive conditions prevailed during ca 7900-4500 cal yr BP. The chironomid record suggests a climate transition between ca 5200 and 4500 cal yr BP to cooler T(July). A distinct cooling trend is evident from ca 4500 until ca 2500 cal yr BP. Thereafter, the study site experienced its coldest conditions (around 4 °C or less) throughout the rest of the Holocene, with the exception of the warming trend during the late 20th century. Beside other factors, the Northern Hemisphere summer insolation seems to be the major driving force for the long-term trends in T(July) at high altitudes in the Eastern Alps. Due to the extreme location of the lake and the limited temperature range represented by the applied calibration data set, the chironomid-based temperature reconstruction fails to track phases of the late-Holocene climatic history with T(July) cooler than 4 °C. Further chironomid-based palaeoclimate model and down-core studies are required to address this problem, provide more realistic T(July) estimates from undisturbed high-altitude lakes in the Alps, and extract a reliable regional temperature signal.
Until recently few studies of amino acid racemization of fossil bivalves and gastropods collected from river terrace deposits in Europe were based on the analysis of the intra-crystalline fraction. Instead they were based on the epimerization (racemization) of a single amino acid, isoleucine, and its inter-conversion to alloisoleucine. This paper presents data from the analysis of the intra-crystalline fraction of the shells, using a preparation technique of sample bleaching to remove the leachable matrix, thus leaving a component that exhibits closed-system behaviour. Reverse-phase HPLC separation with fluorescence detection allows the interpretation of four amino acids in detail: aspartic acid, glutamic acid, alanine and valine. The intra-crystalline fraction offers greater potential for improved resolution, especially when combined with the analysis of multiple amino acid d/l values, which racemize at different rates. This is explored using three species of freshwater gastropods (Bithynia tentaculata and troschelii, Valvata piscinalis) and the bivalve Corbicula. Sites of different ages within the Lower Thames river terrace sequence are used as a stratigraphical framework, with samples from other southern UK sites providing supplementary evidence. The results indicate better resolution using the intra-crystalline fraction over that obtained using unbleached shells, with differentiation possible at sites of up to MIS 7 age. However, for older sites, although values are always higher, the separation is less successful. A species effect has been identified between the gastropod shells. Despite the analysis of intra-crystalline protein, amino acid data from Corbicula remain problematical. Preliminary data on the opercula from Bithynia indicate that better resolution is possible, particularly at older sites.
Aminostratigraphies of Quaternary non-marine deposits in Europe have been previously based on the racemization of a single amino acid in aragonitic shells from land and freshwater molluscs. The value of analysing multiple amino acids from the opercula of the freshwater gastropod Bithynia, which are composed of calcite, has been demonstrated. The protocol used for the isolation of intra-crystalline proteins from shells has been applied to these calcitic opercula, which have been shown to more closely approximate a closed system for indigenous protein residues. Original amino acids are even preserved in bithyniid opercula from the Eocene, showing persistence of indigenous organics for over 30 million years. Geochronological data from opercula are superior to those from shells in two respects: first, in showing less natural variability, and second, in the far better preservation of the intra-crystalline proteins, possibly resulting from the greater stability of calcite. These features allow greater temporal resolution and an extension of the dating range beyond the early Middle Pleistocene. Here we provide full details of the analyses for 480 samples from 100 horizons (75 sites), ranging from Late Pliocene to modern. These show that the dating technique is applicable to the entire Quaternary. Data are provided from all the stratotypes from British stages to have yielded opercula, which are shown to be clearly separable using this revised method. Further checks on the data are provided by reference to other type-sites for different stages (including some not formally defined). Additional tests are provided by sites with independent geochronology, or which can be associated with a terrace stratigraphy or biostratigraphy. This new aminostratigraphy for the non-marine Quaternary deposits of southern Britain provides a framework for understanding the regional geological and archaeological record. Comparison with reference to sites yielding independent geochronology, in combination with other lines of evidence, allows tentative correlation with the marine oxygen isotope record.
Recent recommendations for the expression of time units in Quaternary Science Reviews appear still to leave room for confusion. Here, I propose that the entire palaeoclimate community should agree on the use of a common zero for age scales, with a clear and informative notation. I briefly review the options available in the hope that this will lead to a rapid discussion and conclusion.
On 6 April, 2009, a Mw 6.3 earthquake struck L’Aquila and dozens of neighbouring villages (Abruzzo, central Italy) causing 308 deaths and with thousands injured. Within Italian seismicity, this was the strongest event since 1980 (Irpinia; Mw 6.9), and the first located so close to a large city since 1908 (Messina; Mw 7.3). Consistent data from an integrated approach (including stratigraphy, geomorphology, tephrochronology and paleoseismology) have allowed us to identify a 19-km-long, hitherto poorly known structure as being responsible for this earthquake (Paganica–San Demetrio fault system, PSDFS). The fingerprinting of four well-dated tephra layers and a detailed outline of the geomorphological and stratigraphic setting have provided the basis for assessing the behaviour of the PSDFS since its early activity, here dated at least ca 500 ka, to the present. The slip rate of the structure, calculated over different time windows, has fluctuated slightly ca 0.5 mm/yr. Paleoseismological analyses revealed the traces of the last surface-faulting events; thus, we unambiguously recognise the offset associated with the Mw 6.7 earthquake of 1703, which was previously related to other conterminous structures, along with an older comparable strong event, speculatively ascribed to an event purely known as the AD 801 central Apennine earthquake. This study shows that a long-term to short-term integrated approach is crucial in seismic hazard evaluation, especially when dealing with fault systems that are difficult to trace geomorphically, despite being capable of generating 2009-like earthquakes or even stronger events when conterminous structures are also involved.
Lateglacial and Holocene faunal and stable-isotope records from benthic foraminifers in the eastern Mediterranean Sea (EMS) suggest a high spatiotemporal variability of deep-water oxygenation and biogeochemical processes at the sea floor during that time. Changes in the oxygenation and food availability of the deep-sea ecosystems are closely linked to the hydrology of the EMS borderlands; they reflect orbital and suborbital climate variations of the high northern latitudes and the African monsoon system. During the last glacial maximum, cool surface waters and high evaporation resulted in maximum convection and oxic deep-waters in all sub-basins. Strong wind-induced mixing fostered surface-water production with seasonal phytodetritus fluxes. During the glacial termination and the Holocene, oxygenation and food availability of deep-sea benthic ecosystems were characterized by a pronounced regional differentiation. Local deep-water formation and trophic conditions were particularly variable in the northern Aegean Sea as a response to changes in riverine runoff and Black Sea outflow. During the interval of sapropel S1 formation in the early Holocene, average oxygen levels decreased exponentially with increasing water depth, suggesting a basin-wide shallowing of vertical convection superimposed by local signals. In the northernmost Aegean Sea, deep-water ventilation persisted during the early period of S1 formation, owing to temperature-driven local convection and the absence of low-salinity Black Sea outflow. At the same time, severe temporary anoxia occurred in the eastern Levantine basin at water depths as shallow as 900 m. This area was likely influenced by enhanced nutrient input of the Nile river that resulted in high organic matter fluxes and related high oxygen-consumption rates in the water column. In the southern Aegean and Levantine Seas, we observe a gradual increase in deep-water residence times, preceding S1 formation by approximately 1–1.5 kyr. Once oxygen levels fell below a critical threshold, the benthic ecosystems collapsed almost synchronously with the onset of S1 deposition. The recovery of benthic ecosystems during the terminal phase of S1 formation is controlled by subsequently deeper convection and re-ventilation over a period of approximately 1500 years. After the re-ventilation of the various sub-basins had been completed during the middle and late Holocene, deep-water renewal was more or less similar to recent rates. During that time, deep-sea ecosystem variability was driven by short-term changes in food quantity and quality as well as in seasonality, all of which are linked to millennial-scale changes in riverine runoff and associated nutrient input.
High-resolution macroscopic charcoal and pollen analysis were used to reconstruct an 11 000-year-long record of fire and vegetation history from Beaver Lake, Oregon, the first complete Holocene paleoecological record from the floor of the Willamette Valley. In the early Holocene (ca 11 000–7500 calendar years before present [cal yr BP]), warmer, drier summers than at present led to the establishment of xeric woodland of Quercus, Corylus, and Pseudotsuga near the site. Disturbances (i.e., floods, fires) were common at this time and as a result Alnus rubra grew nearby. High fire frequency occurred in the early Holocene from ca 11 200–9300 cal yr BP. Riparian forest and wet prairie developed in the middle Holocene (ca 7500 cal yr BP), likely the result of a decrease in the frequency of flooding and a shift to effectively cooler, wetter conditions than before. The vegetation at Beaver Lake remained generally unchanged into the late Holocene (from 4000 cal yr BP to present), with the exception of land clearance associated with Euro-American settlement of the valley (ca 160 cal yr BP). Middle-to-late Holocene increases in fire frequency, coupled with abrupt shifts in fire-episode magnitude and charcoal composition, likely indicate the influence anthropogenic burning near the site. The paleoecological record from Beaver Lake, and in particular the general increase in fire frequency over the last 8500 years, differs significantly from other low-elevation sites in the Pacific Northwest, which suggests that local controls (e.g., shifts in vegetation structure, intensification of human land-use), rather than regional climatic controls, more strongly influenced its environmental history.
This study forms part of a wider investigation of late Quaternary environments in the Southern Hemisphere. We here review the terrestrial and near-shore proxy data from Australia, Indonesia, Papua New Guinea (PNG), New Zealand and surrounding oceans during 35–10 ka, an interval spanning the lead-up to the Last Glacial Maximum (LGM), the LGM proper (21 ± 2 ka), and the ensuing deglaciation. Sites selected for detailed discussion have a continuous or near continuous sedimentary record for this time interval, a stratigraphically consistent chronology, and one or more sources of proxy climatic data. Tropical Australia, Indonesia and PNG had LGM mean annual temperatures 3–7 °C below present values and summer precipitation reduced by at least 30%, consistent with a weaker summer monsoon and a northward displacement of the Intertropical Convergence Zone. The summer monsoon was re-established in northwest Australia by 14 ka. Precipitation in northeast Australia was reduced to less than 50% of present values until warmer and wetter conditions resumed at 17–16 ka, followed by a second warmer, wetter phase at 15–14 ka. LGM temperatures were up to 8 °C lower than today in mainland southeast Australia and up to 4 °C cooler in Tasmania. Winter rainfall was much reduced throughout much of southern Australia although periodic extreme flood events are evident in the fluvial record. Glacial advances in southeast Australia are dated to 32 ± 2.5, 19.1 ± 1.6 and 16.8 ± 1.4 ka, with periglacial activity concentrated towards 23–16 ka. Deglaciation was rapid in the Snowy Mountains, which were ice-free by 15.8 ka. Minimum effective precipitation in southern Australia was from 14 to 12 ka. In New Zealand the glacial advances date to ∼28, 21.5 and 19 ka, with the onset of major cooling at ∼28 ka, or well before the LGM. There is no convincing evidence for a Younger Dryas cooling event in or around New Zealand, but there are signs of the Antarctic Cold Reversal in and around New Zealand and off southern Australia. There remain unresolved discrepancies between the climates inferred from pollen and those inferred from the beetle and chironomid fauna at a number of New Zealand sites. One explanation may be that pollen provides a generalised regional climatic signal in contrast to the finer local resolution offered by beetles and chironomids. Sea surface temperatures (SSTs) were up to 5 °C cooler during the LGM with rapid warming after 20 ka to attain present values by 15 ka. The increase in summer monsoonal precipitation at or before 15 ka reflects higher insolation, warmer SSTs and steeper thermal gradients between land and sea. The postglacial increase in winter rainfall in southern Australia is probably related to the southward displacement of the westerlies as SSTs around Antarctica became warmer and the winter pack ice and Antarctic Convergence Zone retreated to the south.
On Spitsbergen, western Svalbard, three major glacial advances have been identified during the Weichselian. All three reached the continental shelf west of the Svalbard archipelago. Radiocarbon, luminescence and amino acid dating of interbedded interstadial and interglacial sediments indicate that these glacial advances have Early (Isotope Stage 5d), Middle (Stage 4), and Late Weichselian ages (Stage 2). An additional, more local, advance has been dated to Isotope Stage 5b. The Late Weichselian ice sheet expanded across the entire Barents Sea. However, in the south-western Barents Sea, the Late Weichselian till is the only till above Eemian sediments, indicating that the Early- and Middle Weichselian ice advances were restricted to the Svalbard archipelago and the northern Barents Sea.A major problem with the onshore sites is the dating of events beyond the range of the radiocarbon method. To overcome this, the onshore record has been correlated with marine cores from the continental slope and the deep-sea west of Svalbard, where a chronology has been established by oxygen isotope stratigraphy. Ice rafted detritus (IRD) was used as the main monitor of glaciation. The IRD record closely mirrors the glaciation history as interpreted from the onshore sections. During the Late Weichselian, the largest IRD peak occurred during deglaciation, a pattern also postulated for the earlier events. Given this, the results from the marine cores indicate that the ages for the first glacial advances during the Weichselian were a few thousand years older than interpreted from the onshore stratigraphy.
The persistence, stability and interhemispheric phasing of the Dansgaard–Oeschger (DO) climate oscillation over the last glacial period (0–100 ka) has been evaluated in oxygen isotope records of three polar ice cores (GRIP, GISP2, and Byrd Station) and a midlatitude deep-sea core from the North Atlantic Ocean (MD95-2042). The results show that DO oscillations in atmospheric conditions occurred in both northern and southern polar ice records, although in the southern records the oscillations had at most only ca. one-tenth the power of those in the north. The DO oscillations first appeared during Marine Isotope Stage (MIS) 4, and the average spectral power of the northern hemisphere DO oscillations increased markedly during MIS 3 (30–38 ka). The DO mode in the GISP2 record is confined to the frequency band 1/(1.59 kyr) to 1/(1.37 kyr), but in the GRIP record, the mode exhibits strong frequency splitting over a band that is wider by ca. 50%. Time-frequency analysis shows that in GRIP the DO mode undergoes a frequency modulation that is phase-locked with the Earth's obliquity cycle; this modulation does not appear in nearby GISP2. In the North Atlantic marine record, DO oscillations behaved somewhat differently, appearing sporadically during MIS 5 and 4. The planktonic DO oscillations increased in spectral power during MIS 3, leading peak power in the GISP2 record by ca. 3 kyr. DO oscillations were relatively stable in all five records during MIS 3; they could not be detected unequivocally in any of the records during the Holocene (0–11 ka). At other times, the DO mode in all of the records was amplitude-modulated by Earth's orbital parameters. Finally, interhemispheric phasing of DO oscillations over 10–90 ka was assessed between the Byrd Station and GISP2 records, and between the benthic and planktonic records of Core MD95-2042. Coherency studies reveal an apparent time lead of Byrd DO oscillations over GISP2 by 384±70 yr (2σ level), and of the North Atlantic benthic over planktonic DO oscillations by 208±33 yr. This apparent time lead of the southern over the northern temperature proxies is likely the consequence of the distinctive harmonic shapes affecting the northern (rectangular) vs. southern (triangular) DO oscillations; the actual northern–southern relationship, as suggested by modelling and other recent data studies, is most probably in simple antiphase (cross phase of 180°).
The competing roles of bedrock uplift and climatic change in the formation of fluvial terraces remain uncertain. Most of recent studies have attributed terrace formation to climatic changes and held that, even in tectonically active settings, climate variations control cycles of terrace planation and abandonment. Based on field investigations of loess-paleosol sequences, magnetostratigraphy and optically stimulated luminescence (OSL) dating, we develop a new chronology for a spectacular flight of terraces along the Yellow River near Lanzhou, China over past 1.24 Ma. All the terraces are strikingly similar in that they have several meters of paleosol developed directly above fluvial deposits on the terrace treads, suggesting that the abandonment of each terrace due to river incision occurs during the transition from glacial to interglacial climates. However, the ages of terraces cluster in two relatively short time periods (1.24–0.86 Ma and 0.13 Ma – present). During the intervening time between 0.86 Ma and 0.13 Ma, terraces either did not form or were not preserved. We suggest that this record indicates that rock uplift rates varied through time and influenced terrace formation/preservation. Thus, our results demonstrate the utility of deep chronologic records from fluvial terraces for deconvolving the effects of tectonics and climate on fluvial incision.
In addition to being of interest to ancient Greek and Roman historians, the site of Philippi, NE Greece, has long been noted in Quaternary circles for providing the longest continuous European pollen record, spanning the last one million years. Here the original age model is re-evaluated and a new marine-terrestrial correlation is proposed. An astronomical calibration procedure, based on a correspondence between changes in certain vegetation elements and March and June perihelion configurations, suggests that the base of the sequence extends back to 1.35 million years ago. The revised chronological framework for the Tenaghi Philippon sequence provides an opportunity to examine the long-term behaviour of individual taxa and vegetation trends within the context of global climate changes. Comparisons reveal a close correspondence between the terrestrial and marine records, in terms of orbital and suborbital variability. However, joint time-frequency analysis of the arboreal pollen record shows that the obliquity and eccentricity/precession signals persist into the ‘100-kyr’ and ‘41-kyr’ worlds, respectively, suggesting the operation of additional climate mechanisms that are independent of high-latitude glacial–interglacial effects. Unlike ice core and marine sequences, no change in the magnitude of interglacial tree population expansions is observed after the Mid-Brunhes Event. Instead, the Tenaghi Philippon record suggests a major shift in the vegetational composition of interglacials after MIS 16, with the establishment of forests of reduced diversity and a ‘modern’ appearance.
The North Iceland shelf bears essential components of the present surface and intermediate circulation of the northern North Atlantic. Instrumental and historical data give evidence of the sensitivity of this domain to broad, regional-scale oceanic and atmospheric anomalies. Our investigation of the paleohydrological variability off Northern Iceland throughout the last 10 000 cal yr suggests that atmospheric forcing alone, through combined changes in strength of the wind stress curl and sea-level atmospheric pressure pattern over the Nordic Seas, is sufficient to explain the recorded changes in origins and dynamics of surface and intermediate water masses. Our biotic proxies, coccoliths and benthic foraminifera, were extracted from a giant piston core (MD99-2269) collected in a shelf trough where sediment accumulated at an excess rate of 2 m/kyr. The mid-Holocene from 6.5 to 3.5 cal kyr BP was a time of peaked carbonate production and subsequent sedimentation, and strong water-column stratification with a thick layer of cold-fresh Arctic surface water overlapping an enhanced flow of Irminger/Atlantic Intermediate water. Applying conditions triggering present-time carbonate plankton blooms in the studied area, we infer that a lowered cyclonic activity associated with decreased winter storms and reduced production of Arctic Intermediate Water in the Iceland Sea were conductive of the recorded mid-Holocene water column structure. The opposite situation (warm Atlantic surface water, low vertically-integrated inflow of Irminger water, abutment of Arctic Intermediate water in deep shelf troughs) characterized the early Holocene as well as a shorter late Holocene period centred at 2 cal kyr BP. The Little Ice Age (ca. 0.2–0.6 cal kyr BP) and a short event at around 3 cal kyr BP stand as times of extreme advection of polar waters and extended sea–ice development. A comparison of the recorded long-term Holocene evolution of water column structure off Northern Iceland with climate and hydrological changes in the north-eastern Atlantic suggests that the strength of Atlantic inflow into the Nordic Seas was subjected to a balance between the Irminger and the Norwegian branches. This balance is thought to be mostly related to changes in the intensity and location of westerly winds and associated atmospheric pressure gradients in the North Atlantic.
As part of a wider study of last glacial and deglacial climates in the Southern Hemisphere continents, we here review terrestrial and near-shore marine records from equatorial and southern Africa between 30,000 and 10,000 years ago (30–10 ka). This time interval covers the lead-up to the Last Glacial Maximum (LGM; 21 ± 2 ka), the LGM proper, and the ensuing deglacial. Records selected for review needed to meet three requirements: continuity or near continuity over the period; a well-established chronology; and at least one but preferably several unambiguous proxy(ies).
Relative sea-level change along the Italian coast and adjacent seas—the combined result of eustasy, glacio-hydro-isostasy and vertical tectonic motion—exhibits considerable spatial and temporal variability throughout the Holocene. The tectonic contribution can be evaluated from the elevation of MIS 5.5 shoreline-markers that are well developed in many localities and the eustatic and isostatic contributions can be predicted from models of ice sheets and earth rheology. Discrepancies between observed Holocene sea levels and model predicted values provide the information for refining the model parameters, including the tectonic rates of vertical movement. Recent and new Holocene and MIS 5.5 information from 30 sites in Italy has been evaluated and compared with model results to calibrate the predictive model. The resulting parameters for the earth rheology and for the eustatic (ice-volume equivalent) sea-level function are consistent with results from regions outside of the Mediterranean and reflect global values. Using the calibrated model parameters the relative sea-level change due to eustasy and the concomitant isostasy is predicted across the central Mediterranean region. Holocene tectonic rates of vertical motion are also given for the Italian coastal zone. At most sites where the MIS 5.5 shoreline occurs above or below its ‘tectonically stable’ position, the inferred rates of vertical crustal displacements are consistent with the assumption that average rates for the past ∼125,000 years are comparable to the average Holocene rates, but at some locations in eastern Sicily and southern Calabria the Holocene rates exceed the longer term average rates.
Quaternary glacial stratigraphy and relative sea-level changes reveal at least four expansions of the Kara Sea ice sheet over the Severnaya Zemlya Archipelago at 79°N in the Russian Arctic, as indicated from tills interbedded with marine sediments, exposed in stratigraphic superposition, and from raised-beach sequences that occur at altitudes up to 140 m a.s.l. Chronologic control is provided by AMS 14C, electron-spin resonance, green-stimulated luminescence, and aspartic-acid geochronology. Major glaciations followed by deglaciation and marine inundation occurred during MIS 10-9, MIS 8-7, MIS 6-5e and MIS 5d-3. The MIS 6-5e event, associated with the high marine limit, implies ice-sheet thickness of >2000 m only 200 km from the deep Arctic Ocean, consistent with published evidence of ice grounding at ∼1000 m water depth in the central Arctic Ocean. Till fabrics and glacial tectonics record repeated expansions of local ice caps exclusively, suggesting wet-based ice cap advance followed by cold-based regional ice-sheet expansion. Local ice caps over highland sites along the perimeter of the shallow Kara Sea, including the Byrranga Mountains, appear to have repeatedly fostered initiation of a large Kara Sea ice sheet, with exception of the Last Glacial Maximum (MIS 2), when Kara Sea ice did not impact Severnaya Zemlya and barely graced northernmost Taymyr Peninsula.
Multiproxy analyses were performed on core MS27PT recovered in hemipelagic sediments deposited on the Nile margin in order to reconstruct Nile River palaeohydrological fluctuations during the last 100,000 years. The strontium and neodymium isotope composition of the terrigenous fraction and the major element distribution reveal large and abrupt changes in source, oscillating between a dominant aeolian Saharan contribution during arid periods and a dominant Nile River contribution during pluvial periods. Iron content shows a strong correlation with strontium and neodymium isotopes. This allows the use of a high-resolution continuous Fe record as a proxy of Blue Nile sediment input over the last 100,000 years. The detailed Fe record, with approximately 10 years resolution during pluvial periods, is consistent with subtropical African records of well-dated lake level fluctuations and thus constitutes a first continuous high resolution record of the East African monsoon regime intensity over Ethiopia.
Identification of the causes of past climate change requires detailed knowledge of one of the most important natural factors—solar forcing. Prior to the period of direct solar observations, radionuclide abundances in natural archives provide the best-known proxies for changes in solar activity. Here we present two independent reconstructions of changes in solar activity during the last 1000 yr, which are inferred from 10Be and 14C records. We analyse the tree-ring 14C data (SHCal, IntCal04 from 1000 to 1510 AD and annual data from 1511 to 1950 AD) and four 10Be records from Greenland ice cores (Camp Century, GRIP, Milcent and Dye3) together with two 10Be records from Antarctic ice cores (Dome Concordia and South Pole). In general, the 10Be and 14C records exhibit good agreement that allows us to obtain reliable estimates of past solar magnetic modulation of the radionuclide production rates. Differences between 10Be records from Antarctica and Greenland indicate that climatic changes have influenced the deposition of 10Be during some periods of the last 1000 yr. The radionuclide-based reconstructions of past changes in solar activity do not always agree with the sunspot record, which indicates that the coupling between those proxies is not as close as has been sometimes assumed. The tree-ring 14C record and 10Be from Antarctica indicate that recent solar activity is high but not exceptional with respect to the last 1000 yr.
This study provides an interpretation of interrelated Quaternary fluvial and aeolian activity related to climate change on Cooper Creek in the Lake Eyre Basin in southwestern Queensland, central Australia. The extensive muddy floodplain is characterised by buried sandy palaeochannels now almost entirely invisible but stratigraphically connected to source-bordering dunes that emerge as distinctive sandy islands through the floodplain surface. Luminescence dating has identified pronounced periods of fluvial activity represented by abundant sandy alluvium from Marine Isotope Stages (MIS) 8–3. While all these sandy fluvial episodes on Cooper Creek were much more powerful than anything subsequent, they appear to be ranked in order of declining activity. MIS 8–6 saw reworking of almost the entire floodplain whereas subsequent phases of reworking were far less extensive. Source-bordering dunes were derived from active sandy channels in late MIS 5 (∼85–80 ka) and mid MIS 3 (50–40 ka). After ∼40 ka sand-channel activity largely ceased and the floodplains and channels were inundated with mud, isolating the dunes as emergent features. Although aeolian reworking of the upper parts of some dunes has continued to the present, they show remarkable resilience, having survived without appreciable migration for at least 40 ka. Whilst the channels once determined the location of source-bordering dunes, in an interesting role reversal the remnant dunes now determine the position of many contemporary flood-channels and waterholes by deflection and confinement of overbank flows.
Core PRAD 1-2, located on the western flank of the Mid-Adriatic Deep, contains a continuous sediment record extending back to upper MIS-11. The upper part of the record which spans the mid Holocene to MIS 5–4 (the last ca 105,000 years) has been investigated for tephra content. A total of 25 discrete tephra layers were discovered, only one of which was visible in the core sequence. The other 24 are not visible to the naked eye, nor were the majority detected by routine down-core scanning methods. A total of 625 geochemical measurements obtained from individual glass shards using WDS-EPMA enabled 21 of the 25 tephras to be assigned to known volcanic events emanating from the Campanian Province (Campi Flegrei, Somma-Vesuvius and Ischia Island). The results provide an independent basis for establishing an age–depth profile for the upper part of the PRAD 1-2 record. This study demonstrates that the number of non-visible tephra layers can significantly exceed the number of visible layers in some deep marine sequences. Routine testing for the presence of non-visible tephra layers can therefore prove rewarding, leading to the detection of additional isochrons for dating and correlating marine sequences, and for their synchronisation with terrestrial records.
Exposure durations of glacial landforms in widely separated areas of central Yukon Territory affected by the northern sector of the Cordilleran Ice Sheet (CIS) and alpine glaciers have been determined using cosmogenic 10Be in quartz. The aim of our research is to test previous reconstructions of glacial history and to begin to address the paucity of chronological control for the lateral and vertical extent of the northern CIS. Chronological evidence for CIS expansion predating the Last Glacial Maximum comes from minimum surface exposure durations of c 100 ka for two bedrock samples within the Reid glacial limit, indicating a possible marine Oxygen Isotope Stage (OIS) 6 age for this event, and from minimum exposure durations of about 40 ka for boulders on moraines constructed by alpine glaciers on a nunatak within the McConnell glacial limit (OIS 2), indicating a possible OIS 4 age. High elevation minimum surface exposure durations within the McConnell limit indicate that some areas formerly mapped as nunataks were covered by cold-based ice prior to 30 ka. Montane glaciation in the Mackenzie Mountains, outside the McConnell glacial limit, was contemporaneous with nearby CIS advance at 17 ka, with CIS retreat by 15 ka. Deglaciation of the Tintina Trench, a major ice discharge route, was completed by 12 ka. At this time ice in an adjacent discharge route to the south was still entering higher-elevation valleys in the Pelly Mountains. A Lateglacial readvance may have peaked at ca 10 ka in the Ogilvie Mountains. Considerable variation in ages from individual landforms, and possible complex histories, require additional cosmogenic nuclide measurements to confirm interpretations.
We use 10Be surface exposure dating to construct a high-resolution chronology of glacial fluctuations in the Sierra Nevada, California. Most previous studies focused on individual glaciated valleys, whereas our study compares chronologies developed throughout the range to identify regional patterns in the timing of glacier response to major climate changes. Sites throughout the range indicate Last Glacial Maximum retreat at 18.8 ± 1.9 ka (2σ) that suggests rather consistent changes in atmospheric variables, e.g., temperature and precipitation, throughout the range. The penultimate glacial retreat occurred at ca 145 ka. Our data suggest that the Sierra Nevada landscape is dominated by glacial features deposited during marine isotope stage (MIS) 2 and MIS 6. Deposits of previously recognized glaciations between circa 25 and 140 ka, e.g., MIS 4, Tenaya, early Tahoe, cannot be unequivocally identified. The timing of Sierra Nevada glacial retreat correlates well with other regional paleoclimate proxies in the Sierra Nevada, but differs significantly from paleoclimate proxies in other regions. Our dating results indicate that the onset of LGM retreat occurred several thousand years earlier in the Sierra Nevada than some glacial records in the western US.
Thirty-eight new cosmogenic (10Be) exposure ages from the Scoresby Sund region of east Greenland indicate that prominent moraine sets deposited by mountain glaciers date from 780 to 310 yr, approximately during the Little Ice Age, from 11 660 to 10 630 yr, at the end of the Younger Dryas cold interval or during Preboreal time, and from 13 010 to 11 630 yr, during lateglacial time. Equilibrium line altitudes (ELAs) interpreted from lateglacial to Early Holocene moraines indicate summertime cooling between ∼3.9 and 6.6 °C relative to today's value, much less than the extreme Younger Dryas cooling registered by Greenland ice cores (mean-annual temperatures of ∼15 °C colder than today's value). This apparent discrepancy between paleotemperature records supports the contention that Younger Dryas cooling was primarily a wintertime phenomenon. 10Be ages of lateglacial and Holocene moraines show that mountain glaciers during the Little Ice Age were more extensive than at any other time since the Early Holocene Epoch. In addition, 10Be ages of lateglacial moraines show extensive reworking of boulders with cosmogenic nuclides inherited from prior periods of exposure, consistent with our geomorphic observations and cosmogenic-exposure dating studies in other Arctic regions.
Temporal and spatial changes in glacier cover throughout the Late Quaternary in Tibet and the bordering mountains are poorly defined because of the inaccessibility and vastness of the region, and the lack of numerical dating. To help reconstruct the timing and extent of glaciation throughout Tibet and the bordering mountains, we use geomorphic mapping and 10Be cosmogenic radionuclide (CRN) surface dating in study areas in southeastern (Gonga Shan), southern (Karola Pass) and central (Western Nyainqentanggulha Shan and Tanggula Shan) Tibet, and we compare these with recently determined numerical chronologies in other parts of the plateau and its borderlands. Each of the study regions receives its precipitation mainly during the south Asian summer monsoon when it falls as snow at high altitudes. Gonga Shan receives the most precipitation (>2000 mm a−1) while, near the margins of monsoon influence, the Karola Pass receives moderate amounts of precipitation (500–600 mm a−1) and, in the interior of the plateau, little precipitation falls on the western Nyainqentanggulha Shan (∼300 mm a−1) and the Tanggula Shan (400–700 mm a−1). The higher precipitation values for the Tanggula Shan are due to strong orographic effects. In each region, at least three sets of moraines and associated landforms are preserved, providing evidence for multiple glaciations. The 10Be CRN surface exposure dating shows that the formation of moraines in Gonga Shan occurred during the early–mid Holocene, Neoglacial and Little Ice Age, on the Karola Pass during the Lateglacial, Early Holocene and Neoglacial, in the Nyainqentanggulha Shan date during the early part of the last glacial cycle, global Last Glacial Maximum and Lateglacial, and on the Tanggula Shan during the penultimate glacial cycle and the early part of the last glacial cycle. The oldest moraine succession in each of these regions varies from the early Holocene (Gonga Shan), Lateglacial (Karola Pass), early Last Glacial (western Nyainqentanggulha Shan), and penultimate glacial cycle (Tanggula Shan). We believe that the regional patterns and timing of glaciation reflect temporal and spatial variability in the south Asian monsoon and, in particular, in regional precipitation gradients. In zones of greater aridity, the extent of glaciation has become increasingly restricted throughout the Late Quaternary leading to the preservation of old (≫100 ka) glacial landforms. In contrast, in regions that are very strongly influenced by the monsoon (≫1600 mm a−1), the preservation potential of pre-Lateglacial moraine successions is generally extremely poor. This is possibly because Lateglacial and Holocene glacial advances may have been more extensive than early glaciations and hence may have destroyed any landform or sedimentary evidence of earlier glaciations. Furthermore, the intense denudation, mainly by fluvial and mass movement processes, which characterize these wetter environments, results in rapid erosion and re-sedimentation of glacial and associated landforms, which also contributes to their poor preservation potential.
Late Quaternary glacier fluctuations in the Macha Khola valley (Gorkha Himal, Nepal) were reconstructed using relative and absolute dating techniques. Our results indicate that younger moraine complexes were left by Late Holocene (<1.7 cal. ka BP), mid-Holocene (ca 3 cal. ka BP), and Lateglacial (ca 13 cal. ka BP) ice advances. Older Late Quaternary glacier advances occurred during Marine Oxygen Isotope Stages (MIS) 2 and 3–4. No relics of Middle or Early Pleistocene glaciations could be found. During MIS 3–4, glaciers advanced down to an altitude of at least 2150 m a.s.l., corresponding to an ELA depression of approximately 1300 m. At about 3500 m a.s.l., the MIS 2 Macha Khola glacier reached almost the thickness of the former MIS 3–4 glacier and retreated some time before 17.9 cal. ka BP. The Lateglacial glacier advanced again several times to altitudes between 2450 and 3400 m a.s.l. The mid-Holocene glaciers extended much farther down-valley than the Late Holocene ones. Dendrochronological data of Abies spectabilis suggested several periods of unfavourable growth conditions especially at the beginning of the 19th (1820) and 20th (1905) centuries.
In this study we present a reconstruction of the global 10Be production rate over the past 250,000 years from three marine sediment cores located in high accumulation environments in the North-, northwest-, and South Atlantic Ocean (ODP Sites 983, 1063 and 1089). The 10Be records are corrected for oceanic transport processes and Principal Component Analysis (PCA) is used to extract the common signal from the three records, which we interpreted as variations of the global 10Be production rate. The reconstruction presented here may serve as (i) a record of past flux of Galactic Cosmic Rays (GCR), (ii) a proxy for past geomagnetic dipole strength, and (iii) as a global matching tool to synchronize marine archives with ice cores and terrestrial records.
A compilation and a critical assessment of the 14C data set available show that the chronology of glacial events in the Pyrenees is not well constrained. After reviewing the literature on glacial reconstruction, we suggest a simplified subdivision of the Pyrenean last glacial cycle record into Last Pleniglacial, Deglaciation, and Neoglacial. To improve the numerical glacial chronology, we provide 10Be surface exposure ages for 5 glacial erosion surfaces, 9 moraines and 2 erratics in the Upper Noguera Ribagorçana Valley (south-central Pyrenees). Published corrected 14C data and new 10Be exposure ages indicate that the major phase of moraine building recorded in this valley during the Last Pleniglacial probably occurred after 25 ka BP. This age calls in question the generally accepted hypothesis of a very early deglaciation of the Pyrenees ca 70–40 ka BP, and strongly suggests that the Pyrenees could have been in pleniglacial conditions during the Last Glacial Maximum (LGM). However, we do not exclude the possibility that the maximum glacier extent during the last glacial cycle had taken place much earlier than the LGM, as indicated by some published U-Th, AMS 14C and OSL data. We suggest that pleniglacial conditions could have taken place during a longer (⪢30–20 ka) period than generally assumed, and that the Last Pleniglacial could include several glacier fluctuations recorded irregularly in different valleys, with a last major glacier readvance taking place around the LGM. In addition, the Deglaciation is represented by a series of moraines deposited between ca 13.7±0.9 and 10.1±0.6 ka. This moraine series indicates a highly variable climatic pattern that is partly correlated with Greenland Stadial 1 (the Younger Dryas), and suggests that the Deglaciation could have continued into the early Holocene.
Evidence is presented from ODP Hole 893A, Santa Barbara Basin for possible synchroneity between Greenland and California Margin submillennial climate change records during Termination 1 and the Last Glacial Maximum (LGM). Planktonic foraminiferal isotope and faunal records are compared to the GISP2 δ18O records (Greenland) for the interval between 30 and 10 ka using a new chronology, based on 38 planktonic 14C dates. Apparent synchronous climatic events include: Interstadial (IS) events 2, 3 and 4; A broad warming trend between 21 and 19 ka and a broad cooling trend between 19 and 17 ka; Bølling and Ållerød warm episodes separated by the cooler Older Dryas event; Younger Dryas cool episode; and the Preboreal. The resulting tight correlation supports an intimate teleconnection between Santa Barbara Basin surface waters and Greenland air temperatures. Differences between Greenland and Santa Barbara Basin suggest that some regional variations were superimposed on the global pattern of climate change (e.g. the Pre-Bølling Warming).
Marine oxygen isotope stage (MIS) 11 has been described as a super-interglacial because of its long duration, more than 30 ka, but this view is often refuted by the observation that the peak sea level and maximum temperature did not surpass other interglacials, including the last interglacial. We address this problem using data from coastal sediments; we conducted diatom and sulfur analyses on two cores of high accumulation rate (0.52 m/ka) sediments from Osaka Bay, Japan. A linear age model applied to the diatom data shows that sea-level variations with precession cycles are correlated with oxygen isotopic events 11.3, 11.24, 11.23, 11.22, and 11.1. Diatom abundances reveal sea level increases and falls because of environmental changes caused by stepwise extension of the bay. This extension can be verified and mapped using data from 15 other drill cores. Sea level was above the sill for Osaka Bay during the marine interval in Osaka Bay, spanning 60 ka. It was above the sill for Kawachi Bay during the marine interval in Kawachi Plain for a duration of 44 ka, including events 11.3 and 11.23. The highest sea level was above the sill for Kyoto Bay during an interval of 16 ka centered at event 11.3. Estimates of sill elevations together with geological data suggest that the sea level of MIS 11 changed within a range from −60 m to +20 m. Palynological data from the same core show that the MIS 11 climate around Osaka Bay was divided into early warm-temperate and late cool-temperate times, with a boundary between events 11.3 and 11.24. During the marine interval in Kyoto, the climate was an extremely warm hypsithermal, almost coincided with the warmest interval in Antarctica where temperatures are >0 °C.
The early part of marine isotopic Stage 11 near 400,000 years ago provides the closest analog to Holocene insolation levels of any interglaciation during the era of strong 100,000-year climatic cycles. The CH4 concentration measured in Vostok ice fell to ∼450 ppb, and CO2 values to ∼250 ppm. These natural decreases contrast with the increases in recent millennia and support the early anthropogenic hypothesis of major gas emissions from late-Holocene farming. During the same interval, δD values fell from typical interglacial to nearly glacial values, indicating a major cooling in Antarctica early in Stage 11. Other evidence suggests that new ice was accumulating during the closest insolation analog to the present day: a major increase in δ18Oatm at Vostok, a similar increase in marine δ18O values, and re-initiation of ice rafting in the Nordic Sea. The evidence permits extended (>20,000 year) intervals of Stage 11 interglacial warmth in the Antarctic and North Atlantic, yet it also requires that this warmth ended and a new glacial era began when insolation was most similar to recent millennia. The Holocene CO2 anomaly was produced only in part by direct anthropogenic emissions; over half of the anomaly resulted from the failure of CO2 values to fall as they had during previous interglaciations because of natural responses, including a sea-ice advance in the Antarctic and ice-sheet growth in the northern hemisphere.
Combined paleontological, morphostratigraphic and geochronologic data from emerged Middle Pleistocene coastal deposits in Mejillones Peninsula (23°S), northern Chile, strongly suggest that climatic conditions were particularly warm during the particularly warm during the Oxygen Isotope Stage 11 high seastand episode. An anomalous warm-water molluscan assemblage from localities assigned to that interglaciation included several extralimital species, presently living only north of 6°S (or 14°S), that were not present in the area during subsequent Middle and Late Pleistocene, or Holocene, interglacial episodes. Only two of these extralimital species may be found nowadays at the 23°S latitude, in a protected locality, immediately after the occurrence of strong El Niño events. Many of the species of the thermally anomalous molluscan assemblage (TAMA) are the same as those which lived in a closed shallow lagoon near Santa, north-central Peru (9°S) during a brief mid-Holocene episode. The new findings thus indicate that lagoonal and protected embayments were significantly warmer than the open marine environment ca. 400 ka. Actually, the co-occurrence of cool water fauna in exposed sectors of the coastline at that time suggests that the coastal upwelling activity and the Humboldt Current effects were not strongly reduced. The warm-water conditions prevailing in lagoons and protected bays during the Mid-Brunhes episode may reflect particularly warm air temperatures and distinct ocean-atmosphere relationships than those prevalent nowadays. These data support the hypothesis that the Oxygen Isotope Stage 11 was the warmest interglaciation, at least in the southern hemisphere.
Classification of coastal cave environments. Note that sinkholes are commonly known as cenotes in Mexico, and this nomenclature is occasionally extended to other global localities.  
Global subterranean locations where foraminifera that have been recovered. As reported by: Birstein and Ljovuschkin (1965), Mikhalevich (1976), Sket and Iliffe (1980), Reiswig (1981), Rasmussen and Brett (1985), Longly (1986), Proctor and Smart (1991), Novosel et al. (2002), Javaux and Scott (2003), McMurtry et al. (2007), Kitamura et al. (2007), Denitto et al. (2007), Lewis and Tichenor (2008), E. Reinhardt (Oman – Pers. Com., 2009), van Hengstum et al. (2008, 2009). Foraminifera have yet to be documented in southern hemisphere coastal cave environments.  
Surface sediment locations across Bermuda (A) and along the Walsingham Tract (B). Base map and contours (20 m interval) after Vacher et al. (1989).  
The dendrogram produced through Q-mode cluster analysis indicates five separate assemblages of coastal foraminifera in Bermuda. In the Lagoon Assemblage, note how statistically similar the modern littoral cave and Calonectris Pocket A is to other lagoon samples. Sample label prefixes (coastal environments): MA-mangrove, RE-reef, LA-lagoon, AC-anchialine cave, LP-protected lagoon. Sample label suffixes (Bermudian locales): HB-Hungry Bay, MS-Mill Share, N-North Lagoon traverse, MB-Mangrove Bay, H-Hog Breaker Reef, T-Twin Reef, D-Devonshire dock, C-Crystal Cave, L-Leamington Cave, W-Walsingham Cave, W-Walsingham Bay.  
Two hypotheses have been proposed to explain the origin of marine isotope stage (MIS) 11 deposits in small Bermudian caves at +21 m above modern sea level: (1) a +21 m MIS 11 eustatic sea-level highstand, and (2) a MIS 11 mega-tsunami event. Importantly, the foraminifera reported in these caves have yet to be critically evaluated within a framework of coastal cave environments. After statistically comparing foraminifera in modern Bermudian littoral caves and the MIS 11 Calonectris Pocket A (+21 m cave) to the largest available database of Bermudian coastal foraminifera, the assemblages found in modern littoral caves – and Calonectris Pocket A – cannot be statistically differentiated from lagoons. This observation is expected considering littoral caves are simply sheltered extensions of a lagoon environment in the littoral zone, where typical coastal processes (waves, storms) homogenize and rework lagoonal, reefal, and occasional planktic taxa. Fossil protoconchs of the Bermudian cave stygobite Caecum caverna were also associated with the foraminifera. These results indicate that the MIS 11 Bermudian caves are fossil littoral caves (breached flank margin caves), where the total MIS 11 microfossil assemblage is preserving a signature of coeval sea level at +21 m. Brackish foraminifera (Polysaccammina, Pseudothurammina) and anchialine gastropods (∼95%, >300 individuals) indicate a brackish anchialine habitat developed in the elevated caves after the prolonged littoral environmental phase. The onset of sea-level regression following the +21 m highstand would first lower the ancient brackish Ghyben-Herzberg lens (<0.5 m) and flood the cave with brackish water, followed by drainage of the cave to create a permanent vadose environment. These interpretations of the MIS 11 microfossils (considering both taphonomy and paleoecology) are congruent with the micropaleontological, hydrogeological and physical mechanisms influencing modern Bermudian coastal cave environments. In conclusion, we reject the mega-tsunami hypothesis, concur with the +21 m MIS 11 eustatic sea-level hypothesis, and reiterate the need to resolve the disparity between global marine isotopic records and the physical geologic evidence for sea level during MIS 11.
The latter part of the Last Glacial Interval (LGI; 60,000 to 11,700 years ago) experienced a range of climatic and environment extremes. To elucidate the mechanisms of these changes requires records of past variability that are precisely dated and correlated on the same absolute timescale. However, despite decades of research, it is still not possible to align most marine and terrestrial records of past change with ice-core records, largely because of ongoing uncertainties over the conversion of pre-Holocene 14C ages on to a calendar timescale and uncertainties with in ice-core chronologies. As a result, it is equivocal whether climate changes in both hemispheres during the LGI led, lagged or were synchronous with one another. A decadally-resolved radiocarbon calibration is urgently required to test these models of the Earth system. Here we report radiocarbon measurements obtained from subfossil New Zealand kauri (Agathis australis) spanning a collective 3500 years dated between 25,000 and 45,000 years ago. The results are compared to the recently published international calibration curve IntCal09 and to the marine Cariaco Basin datasets. We show that kauri have considerable potential for development of a Southern Hemisphere component of a unified global calibration curve suite, and that tree-ring sequences can be superposed on other radiocarbon records to constrain atmospheric–marine offsets and precisely test the synchronicity of abrupt climate change.
Analyses of plant macrofossils, peat humification and testate amoebae were used to reconstruct a proxy climate record spanning the last 7500 years from an ombrotrophic bog, Temple Hill Moss, in southeast Scotland. The plant macrofossil data were subjected to detrended correspondence analysis (DCA) which modelled effectively the significant wet shifts within the record. A mean water table depth transfer function was applied to the testate amoebae data to provide quantifiable changes. The three proxy records show coherent phase changes which are interpreted as variability in past effective precipitation. Two tephra horizons (Glen Garry and Lairg A) were used in conjunction with radiocarbon dates to construct an age/depth model, producing a robust geochronology from which a time series was calculated. The palaeoclimatic reconstruction identified major wet shifts throughout the Holocene, with specific events occurring around cal. 6650, 5850, 5300, 4500, 3850, 3400, 2800–2450, 1450–1350 and 250–150 BP. Spectral analysis of the plant macrofossil DCA and colorimetric humification data produced a millennial scale periodicity of 1100 years. The same periodicity has also been found in a palaeoclimatic reconstruction from a site in Cumbria (Walton Moss), and may be linked with millennial scale periodicities found in oceanic palaeoclimatic records.
During the Late Pliocene–Middle Pleistocene, 56 species and 15 genera of elongate, cylindrical benthic foraminifera disappeared from the deep sea in the South China Sea (ODP Sites 1143 and 1146) as part of the last global extinction in the deep sea. This extinction group (Ext. Gp) exhibited a pulsed decline in abundance and species richness mostly during glacials, and often associated with periods of expansion of polar ice that resulted from increased cooling of the Earth's climate since ∼2.5 Ma, particularly during the Mid-Pleistocene Climate Transition (MPT, 1.2–0.6 Ma). We infer that the Ext. Gp decline in abundance and disappearance was a result of the increased glacial cooling and consequent increased ventilation of the deep-sea water masses. The detailed record of withdrawal of the Ext. Gp differs between the two sites, with far more disappearances occurring prior to the MPT in the deeper Site 1143 (2772 m) than in the shallower Site 1146 (2092 m). The Late Pliocene and Early Pleistocene declines in deeper parts of the South China Sea (Site 1143) may have resulted from enhanced glacial production of deep, southern-sourced water passing over the sill into the basin from the North-west Pacific. During the MPT however, the Ext. Gp declines and disappearances were of similar timing and magnitude in both sites, implying that both were influenced by the same deep-water mass during glacials at this time. This could have been North Pacific Deep Water, which many workers infer was formed in the northern Pacific during the last glacial, and may have begun forming during MPT glacials, in association with the progressively enhanced cooling of the Northern Hemisphere.
The last glacial maximum (LGM) outline and subsequent retreat pattern (21–7 kyr) of North American ice sheets are reasonably well established. However, the evolution of the ice sheets during their build-up phase towards the LGM between 115 and 21 kyr has remained elusive, making it difficult to verify numerical ice sheet models for this important time interval. In this paper we outline the pre-LGM ice sheet evolution of the Laurentide and Cordilleran ice sheets by using glacial geological and geomorphological records to make a first-order reconstruction of ice sheet extent and flow pattern. We mapped the entire area covered by the Laurentide and Cordilleran ice sheets in Landsat MSS images and approximately 40% of this area in higher resolution Landsat ETM+ images. Mapping in aerial photographs added further detail primarily in Quebec-Labrador, the Cordilleran region, and on Baffin Island. Our analysis includes the recognition of approximately 500 relative-age relationships from crosscutting lineations. Together with previously published striae and till fabric data, these are used as the basis for relative-age assignments of regional flow patterns. For the reconstruction of the most probable ice sheet evolution sequence we employ a stepwise inversion scheme with a clearly defined strategy for delineating coherent landforms swarms (reflecting flow direction and configuration), and linking these to previously published constraints on relative and absolute chronology. Our results reveal that ice-dispersal centres in Keewatin and Quebec were dynamically independent for most of pre-LGM time and that a massive Quebec dispersal centre, rivalling the LGM in extent, existed at times when the SW sector of the ice sheet had not yet developed. The oldest flow system in eastern Quebec-Labrador (Atlantic swarm had an ice divide closer to the Labrador coast than later configurations). A northern Keewatin-Central Arctic Ice Sheet existed prior to the LGM, but is poorly chronologically constrained. There is also evidence for older and more easterly Cordilleran Ice Sheet divide locations than those that prevailed during the Late Wisconsinan. In terms of ice sheet build-up dynamics, it appears that “residual” ice caps after warming phases may have played an important role. In particular, the location and size of remnant ice masses at the end of major interstadials, i.e. OIS 5c and 5a, must have been critical for subsequent build-up patterns, because such remnant “uplands” may have fostered much more rapid ice sheet growth than what would have occurred on a fully deglaciated terrain. The ice-sheet configuration during stadials would also be governed largely by the additional topography that such “residual” ice constitutes because of inherent mass balance–topography feedbacks.
The Sodmein cliff foot cave is the present-day remnant of an ancient cavity, probably of karstic origin. Physical breakdown of the limestone bedrock, rather than solution, has governed its subsequent evolution. Long before 115 ka BP an estimated 8000 m3 of debris came off the weathered roof and mixed with contemporaneous cliff rockfall. Over 4 m of sediments have since accumulated. Wet conditions outside the cave during isotopic stage 5e are documented by sedimentary properties of the J-complex and by its detailed botanical and faunal content. These wet conditions were of regional significance. Shortly after 115 ka BP further subsidence of the roof of the ancient cave led to the present-day cave form. The cave interior has remained dry up to the present, but the deposits indicate an increase of animal passage and plant growth around 25 ka BP and during the Holocene interglacial. The latter period was rather arid in absolute terms, receiving less precipitation under a less regular pluvial regime, compared with the interglacial during isotopic stage 5e.
High-resolution quantitative temperature records are needed for placing the recent warming into the context of long-term natural climate variability. In this study we present a quantitative high-resolution (9-year) summer (June–August) temperature reconstruction back to AD 1177 for the south-eastern Swiss Alps. This region is a good predictor for summer temperatures in large parts of western and central Europe. Our reconstruction is based on a combination of the high-frequency component of annually resolved biogenic silica (bSi flux) data and the low-frequency component of decadal chironomid-inferred temperatures from annually laminated well dated sediments (varves) from proglacial Lake Silvaplana, eastern Swiss Alps.
One or more of three intense and persistent droughts impacted some Native American cultures in the early-11th, middle-12th and late-13th centuries, including the Anasazi, Fremont, Lovelock, and Mississippian (Cahokian) prehistorical cultures. Tree-ring-based reconstructions of precipitation and temperature indicate that warm drought periods occurred between AD 990 and 1060, AD 1135 and 1170, and AD 1276 and 1297. These droughts occurred during minima in the Pacific Decadal Oscillation and may have been associated with positive values of the Atlantic Multidecadal Oscillation. Each of the Native American cultures was supported, to a greater or lesser degree, by precipitation-dependent resources. Both the Four Corners region and Cahokia were sites of intense growth between about AD 1050 and 1130, and by AD 1150, cultures in both regions were undergoing stress. By AD 1300 the Anasazi and Fremont cultures had collapsed and their residual populations had either left their homelands or withered. In the case of Fremont populations, the AD 990–1060 drought may have had the greatest impact. This drought also may have affected the Anasazi, for it was at the end of this drought that some people from Chaco migrated to the San Juan River valley and founded the Salmon Ruin great house. Detailed data do not exist on the number of Lovelock habitation sites or populations over time; however, Lovelock populations appear to have retreated from the western Great Basin to California by AD 1300 or shortly thereafter.
Sedimentary records from California's Northern Channel Islands and the adjacent Santa Barbara Basin (SBB) indicate intense regional biomass burning (wildfire) at the Ållerød–Younger Dryas boundary (∼13.0–12.9 ka) (All age ranges in this paper are expressed in thousands of calendar years before present [ka]. Radiocarbon ages will be identified and clearly marked “14C years”.). Multiproxy records in SBB Ocean Drilling Project (ODP) Site 893 indicate that these wildfires coincided with the onset of regional cooling and an abrupt vegetational shift from closed montane forest to more open habitats. Abrupt ecosystem disruption is evident on the Northern Channel Islands at the Ållerød–Younger Dryas boundary with the onset of biomass burning and resulting mass sediment wasting of the landscape. These wildfires coincide with the extinction of Mammuthus exilis [pygmy mammoth]. The earliest evidence for human presence on these islands at 13.1–12.9 ka (∼11,000–10,900 14C years) is followed by an apparent 600–800 year gap in the archaeological record, which is followed by indications of a larger-scale colonization after 12.2 ka. Although a number of processes could have contributed to a post 18 ka decline in M. exilis populations (e.g., reduction of habitat due to sea-level rise and human exploitation of limited insular populations), we argue that the ultimate demise of M. exilis was more likely a result of continental scale ecosystem disruption that registered across North America at the onset of the Younger Dryas cooling episode, contemporaneous with the extinction of other megafaunal taxa. Evidence for ecosystem disruption at 13–12.9 ka on these offshore islands is consistent with the Younger Dryas boundary cosmic impact hypothesis [Firestone, R.B., West, A., Kennett, J.P., Becker, L., Bunch, T.E., Revay, Z.S., Schultz, P.H., Belgya, T., Kennett, D.J., Erlandson, J.M., Dickenson, O.J., Goodyear, A.A., Harris, R.S., Howard, G.A., Kloosterman, J.B., Lechler, P., Mayewski, P.A., Montgomery, J., Poreda, R., Darrah, T., Que Hee, S.S., Smith, A.R., Stich, A., Topping, W., Wittke, J.H. Wolbach, W.S., 2007. Evidence for an extraterrestrial impact 12,900 years ago that contributed to the megafaunal extinctions and Younger Dryas cooling. Proceedings of the National Academy of Sciences 104, 16016–16021.].
Palaeoclimatic changes through the last 1200 calibrated years have been documented by high-resolution multi-proxy studies of three cores from about 400 m water depth on the North Icelandic shelf. Benthic and planktonic foraminiferal assemblages and stable isotope values, as well as ice rafted debris (IRD) concentrations, are compared with diatom-based sea-surface water temperatures and the reconstructed mean temperature for the Northern Hemisphere. Changes in surface and bottom water characteristics are mainly due to variations in the strength of the relatively warm, high-salinity Irminger Current and the cold East Icelandic Current. The time period between 1200 and around 7–800 cal. (years) BP, including the Medieval Warm Period, was characterized by relatively high bottom and surface water temperatures due to the inflow of Atlantic water masses. After that, a general temperature decrease in the area marks the transition to a period with increased influence of the East Icelandic Current and, at the sea floor, the Norwegian Sea Deep Water. This corresponds to the transition to the Little Ice Age. After about 3–400 cal. BP, the inflow of cold East Icelandic Current was further enhanced. In particular, this had a strong influence on the surface waters, while the sea floor was under some influence of Atlantic water masses, resulting in stratification of the water masses. There is no clear indication of any warming in the area during the last decades.
Calcite speleothems are a hitherto hardly documented occurrence in the nowadays arid to hyper-arid rain-shadow Dead Sea area of eastern Israel. Speleothem ages (U–Th) from two caves on the Dead Sea Fault Escarpment and two caves from arid rain-shadow areas surrounding the Dead Sea, span the last three glacial cycles from ca 354 to 12 ka and suggest episodic moist local palaeoclimate mainly during glacial periods of Marine Isotopic Stages (MIS) 6 and 4 to 2.Previously reported U–Th ages of stromatolites deposited in the Late Pleistocene Lake Lisan and preserved in caves of the Dead Sea Fault Escarpment, suggest that regional relatively moist climate affected the lake catchment area during the late part of (relatively warm) MIS-3 lasting until middle (cold) MIS-2, as well as at the MIS-5 to 4 (interglacial–glacial) transition.Speleothem deposition periods spanning the 38.4 ± 0.5 to 16.4 ± 0.3 ka time interval, i.e. late MIS-3 to early MIS-2, representing moist periods in the lake area, are coeval to regional moist conditions inferred by the stromatolite record. A direct connection is thus implied between local and regional climate at the latest Pleistocene based on correlation between two independent data sets. This connection implies that glacial climate has generally been moister than interglacial climate during the last glacial–interglacial cycle at both local and regional scales around the Dead Sea and its predecessors.
Water isotope records from the EPICA Dronning Maud Land (EDML) and the NorthGRIP ice cores have revealed a one to one coupling between Antarctic Isotope Maxima (AIM) and Greenland Dansgaard-Oeschger (DO) events back to 50 kyr. In order to explore if this north–south coupling is persistent over Marine Isotopic Stage 5 (MIS 5), a common timescale must first be constructed.Here, we present new records of δ18O of O2 (δ18Oatm) and methane (CH4) measured in the air trapped in ice from the EDML (68–147 kyr) and NorthGRIP (70–123 kyr) ice cores. We demonstrate that, through the period of interest, CH4 records alone are not sufficient to construct a common gas timescale between the two cores. Millennial-scale variations of δ18Oatm are evidenced over MIS 5 both on the Antarctic and Greenland ice cores and are coupled to CH4 profiles to synchronise the NorthGRIP and EDML records. They are shown to be a precious tool for ice core synchronisation.With this new dating strategy, we produce the first continuous and accurate sequence of the north–south climatic dynamics on a common ice timescale for the last glacial inception and the first DO events of MIS 5, reducing relative dating uncertainties to an accuracy of a few centuries at the onset of DO events 24 to 20. This EDML-NorthGRIP synchronisation provides new firm evidence that the bipolar seesaw is a pervasive pattern from the beginning of the glacial period. The relationship between Antarctic warming amplitudes and their concurrent Greenland stadial duration highlights the particularity of DO event 21 and its Antarctic counterpart. Our results suggest a smaller Southern Ocean warming rate for this long DO event compared to DO events of MIS 3.
Oxygen and carbon isotopic variations in the upper section of a stalagmite (SF-1) from Buddha Cave (33°40′N 109°05′E) dated by 230Th/234U 210Pb and lamination counting to a time resolution as fine as 1–3 years have recorded climate changes in central China for the last 1270 years. The changes include those corresponding to the Medieval Warm Period Little Ice Age and 20th-century warming lending support to the global extent of these events. The isotopic records also show cycles of 33, 22, 11, 9.6, and 7.2 years. The 33-year cycle could well represent the ∼35-year periodicity of climate fluctuations previously recognized in China and Europe. Cycles of 22, 11, and 9.6 years have often been associated with the Sunspot or lunar-orbit variations. The 7.2-year cycle was recently identified also in tree-ring records from an area close to Buddha Cave. These cycles suggest that external forcing (e.g. solar irradiance) may affect the summer monsoon over eastern China. The general consistency between the climate characteristics inferred from the stable isotope records of SF-1 and those from other proxy records underscores the value of stalagmites as recorders of paleoclimate.
The anthropogenic explanation for the increase in atmospheric methane concentration during the last 5000 years requires large CH4 emissions from human activities beginning early in the Bronze Age. This paper presents a compilation of 311 archeological sites in rice-growing regions of China. The number of new sites between 6000 and 4000 years ago increased almost ten-fold compared with those during previous millennia. This early spread of rice production across most of the area in China where irrigated rice is grown today supports the hypothesis that early farming caused the anomalous methane reversal.
Foraminiferal stable isotopes and assemblages from Franz Victoria and St. Anna troughs provide a valuable record of freshwater and Atlantic Water flows to the northern Barents and Kara seas from deglaciation to present. The δ18O and δ13C of planktonic Neogloboquadrina pachyderma (s) and benthic Elphidium excavatum were up to 1.4‰ lower than present at ca 13, 11.5, and 10 14C ka (global sea-level corrected), mostly reflecting substantial freshwater inputs coincident with glacial–marine sediment deposition. Cassidulina teretis exceeded 40% of benthic foraminifera ca 13 and 10 14C ka, indicating subsurface penetrations of Atlantic Water. The transition to postglacial marine conditions is marked by a ∼1‰ rise in foraminiferal δ18O and a sharp fall in % C. teretis soon after 10 14C ka. These changes imply reduced inputs of freshwater and Atlantic Water. Subsequent isotopic and foraminiferal assemblage variations reflect changing Atlantic Water conditions “upstream” in the Nordic Seas and shifts between the warm Fram Strait and cold Barents Sea branches of Atlantic Water. We hypothesize that glacial-isostatically induced deepening by up to ∼150 m influenced Atlantic Water inflows to the northern Barents Sea during deglaciation and the Holocene. Thus, effects of isostatic recovery have to be factored into paleoceanographic reconstructions.
Top-cited authors
Marie-France Loutre
  • PAGES (Past Global Changes)
André Berger
  • Université Catholique de Louvain - UCLouvain
S. Olander Rasmussen
  • University of Copenhagen
Harry John B Birks
  • University of Bergen
John T. Andrews
  • University of Colorado Boulder